Applying a coating to materials to make them water repellent or waterproof has been practiced in various industries. For example, U.S. Pat. Nos. 4,255,489, 5,348,760, 5,964,934 and 6,268,423 have disclosed methods to coat the building material with different silicone compound, including silicone polymers, poly-metric siloxanes, reactive silane monomers, siliconates and other organic silicon-containing materials to make building materials water resistant. U.S. Pat. Nos. 2,040,818, 3,382,170, 4,175,159, and 5,302,570 have further disclosed methods to coat perlite, vermiculite or diatomite with silicone as the oil absorbent. The disclosures of U.S. Pat. Nos. 2,040,818, 3,382,170, 4,175,159, 4,255,489, 5,302,570, 5,348,760, 5,964,934 and 6,268,423 are hereby incorporated in this application by reference.
The commonality of the coating methods disclosed by the above references is the utilization of the wet-coating method, in which the silicone compound is dissolved or thinned with liquid solvent and the mixed solution or emulsion is sprayed onto the targeted mineral. Then the soaked mineral is dried at certain temperature. The silicone compound emulsion is available in commercial products, such as Dow Corning 36, 346, 39 or 349 emulsions, Union Carbide L45 emulsions, or General Electric SM 62 or 2163 emulsions, etc. In general, with the wet-coating method, the weight of the consumed silicone compound takes a few percent of the target minerals. In other words, to coat 1 ton of the porous mineral, such as perlite, would require about 5 to 40 kilograms of silicone compound to achieve a reasonable result. As shown in U.S. Pat. No. 4,175,159, if less silicone compound is used, the water repellent effect may be faded, because some surfaces may not be coated.
Another drawback with the wet-coating method is that, even using the optimized process as disclosed in U.S. Pat. No. 4,175,159, the cost of the silicone compound remains to be a significant part of the total cost for manufacturing silicone-treated porous natural minerals, as the thickness of the silicone layer generated by the wet-coating method is usually in the range of several micro meters and lots of raw materials are wasted.
Therefore, it is an object of the present invention to provide economical methods to coat the silicone on the porous natural minerals, which consumes less silicone compound and is useful for large scale manufacturing.
It is another object of the present invention to provide a method to coat silicone on the porous natural minerals that can use recycled silicone materials, such as silicone rubber mold, pipe, board, etc.
It is yet another object of the present invention to provide a method to integrate the coating process with the thermal expansion of the perlite or vermiculite so that as little energy is used as possible.
It is still a further object of the present invention to provide a method to form a uniform silicone layer on both main surface and subsurface of porous mineral grains, such that even if the grains are crushed, the hydrophobic and oleophilic attributes would remain.